Integrated circuits formed on silicon dice have become one of the most import hardware foundations of modern technologies. In general, a die includes a plurality of circuit blocks, which are also known as silicon intellectual properties (IP's). For example, central processing units and micro control units are commonly adopted logic circuit blocks. Also, non-volatile and/or volatile embedded memories which can be integrated into a die have become essential circuit blocks in modern dice.
The circuit blocks of a die need to communicate with each other; for optimal efficiency of communication, each of the circuit blocks is equipped with a parallel interface of multiple pins coupled to other circuit block(s). For example, a parallel interface of a memory includes multiple address pins and multiple data pins; each of the address pins can simultaneously receive a portion (such as a binary bit) of an address, so a complete address for accessing the memory is obtained by collecting the portions respectively received by the address pins. For programming (writing) a data to the address of the memory, each data pin of the parallel interface simultaneously receives a portion (such as a binary bit) of the data, thus the complete data is gathered and programmed (written) into a memory location assigned by the address. To read a data from the address of the memory, each of the data pin simultaneously outputs a portion of the data, thus the complete data stored in the address is obtained and outputted through the parallel interface of the memory.
While a parallel interface of a circuit block enhances communication efficiency, it is difficult to perform function test for the circuit block through its parallel interface. Testers equipped with probing cards are used to test dice on silicon wafers; each probing card has multiple probes, each probe can contact to a pad of a die, such that signal and/or power can be fed into the die and/or received from the die. A probe can not contact to a pin unless the pin is connected to a pad, since a pin is merely an internal conduction path within a die for relaying and routing signal. That is, if a circuit block in a die is tested through parallel pins of the parallel interface, each of the parallel pins needs to be connected to an individual pad of the die. Arranging pads for pins of a parallel interface is very expensive, since each pad, e.g., a pad with electro-static discharge (ESD) protection, occupies a considerable layout area of a die. Furthermore, testing through parallel interface constrains efficiency of testing. Because a probing card only has a finite number of probes, more pads a die need to be probed, less dice can be simultaneously tested by a probing card.